In order for infant vision testing procedures to aid substantially in the detection, management and treatment of pediatric ocular disorders, these procedures can be rapid and reliable and provide clinically meaningful results. The psychophysical technique, preferential looking (PL), has been shortened for clinical use in several different procedures, but most demonstrate statistical or practical shortcomings. We propose to evaluate a rapid threshold estimation procedure, the transformed up-down staircase, that we have modified and use with preliminary success in a large sample of young patients with ocular disorders. Refinements of this staircase procedure will be developed to decrease variability and increase utility with all ages of infants. Visual acuity for grating stimuli, measured by PL, is a sensitive index of visual impairment in some disorders (e.g. anisometropic amblyopia), but is less sensitive in other disorders (e.g. strabismic amblyopia). This may be due to more effective use of extrafoveal retina or relatively greater impairment of sensitivity for phase (complex forms) than for spatial frequency and contrast (gratings). These findings may also be generalizable to patients with specific loss of central vision due to anatomatical abnormalities of the globe. We propose to investigate stimulus variations in these and other ocular disorders that may increase the diagnostic potential of PL acuity assessment. In addition, we will continue to trace visual acuity development in infants who are at risk for amblyopia, monitoring the effects of treatment for amblyopia in order to evaluate "sensitive periods" for human visual development.